Hi Again

[mlinder]

Was a member here a while back, but looks like I was purged.

I own a 78 gs550 and an 80 gs550.

I looked around the site again, but didn't stumble on the answer.

Perhaps you can help.

There is a top-end off of an 8 valve gs650g available near me. Can I plant the top end on the gs550 lump? I've heard before that this is true, but I better ask the experts before I pull the trigger.

Thanks,

Mark

[hampshirehog]

Hi. Can be done but a bit of work. Check out the work by SuzukiDon (including his recent woes) for the low down.

[mlinder]

Ah, yes, just found Suzuki_dons posts regarding this issue.

I need to find the 'woe' part, to see if I should do this or not...

[hampshirehog]

Here it is:

http://www.thegsresources.com/_forum/showthread.php?t=164443

[mlinder]

Well, I've gone ahead and done it.
GS650g head, cams, jugs, pistons and cam-cover.

This should be fun.

[mlinder]

OK, saw this question asked, but not answered..

Are exhaust ports and spacing the same on the GS650g head as they are on the gs550e?

[Suzuki_Don]

Well, I've gone ahead and done it.
GS650g head, cams, jugs, pistons and cam-cover.

This should be fun.

That was quick, it took me months to do mine.

[Nessism]

That was quick, it took me months to do mine.

I doubt he installed the parts yet, just bought them.

[mlinder]

Aye, picking up the parts this weekend.

I think it will probably be the most efficient 130 dollars I have ever spent for performance upgrades.

I'm so used to throwing thousands at the racebikes-in-progress for real improvements, or many hundreds at my streetbikes for only moderate improvements, that these parts, and really what appears to be a minimal amount of work, especially since it's already been done and documented by others (Suzuki_Don), that I just couldn't pass the opportunity up.

Plans include a slight shaving of the head for a small bump in compression.

What will be most fun, is that the bike is going to look more or less stock.
1980 GS, with spoked wheels from the 78, the 650 parts attached to the 78's engine, I'll do some inexpensive but effective suspension upgrades, minor aesthetic tweaks will happen, and I'll probably do a bit of unobtrusive frame bracing, a la Yoshis race gs750 (you can barely tell it's there.)
Add what appears to be something like a 40% increase in power to what appears to be an essentially stock 550... and yeah, that has me excited. For 130 bucks in parts..
I love the fact that I'll have kickstart and 6 gears, too

Will keep ya updated!

[mlinder]

It's not going to look much different than it does now, other than cleaned up, painted, and some new 4 into 2's on it.

With 70ish HP. Fun.



I'm looking for ways to lighten it a bit as best I can, but these are so overbuilt, and that excess seems to be intrinsic to it's design, that finding things to remove is pretty hard.

[mlinder]

Picked up the jugs, head, pistons, cams and camcover this weekend.
Also put progressive springs up front and some new shocks out back. Putting a new 2 extra teeth sprocket out back this week.
Will start tearing into the 78 motor this week to get it ready for the new top end. Will shave the head .010 or .020 for a little bump in compression, will lose the starter and make it kickstart only.
70hp gs550 coming soon

I think we are going to do a similar thing to my friends 550. Little different, though. 650 jugs bored to accept 750 pistons. Stock 550 head (the 78, he likes the VM carbs better) with stock cams. Head shaved, should bump up compression a bit with that and staying with the stock combustion chambers from the 550.

That'll put him at 740ish cc's. Should make close to the same power, little more low end, little less top end.

Wont start that one for a bit, though.

[Nessism]

Picked up the jugs, head, pistons, cams and camcover this weekend.
Also put progressive springs up front and some new shocks out back. Putting a new 2 extra teeth sprocket out back this week.
Will start tearing into the 78 motor this week to get it ready for the new top end. Will shave the head .010 or .020 for a little bump in compression, will lose the starter and make it kickstart only.
70hp gs550 coming soon

I think we are going to do a similar thing to my friends 550. Little different, though. 650 jugs bored to accept 750 pistons. Stock 550 head (the 78, he likes the VM carbs better) with stock cams. Head shaved, should bump up compression a bit with that and staying with the stock combustion chambers from the 550.

That'll put him at 740ish cc's. Should make close to the same power, little more low end, little less top end.

Wont start that one for a bit, though.

Sounds like a couple of fun projects!

The CV heads have larger ports so it's not all about the carbs. And you need to watch the compression ratio using big bore kits and stock heads so you guys might want to do some research on the overbore 650 cylinder business.

Good luck and please upload lots of photos for us as you go along!

[mlinder]

Sounds like a couple of fun projects!

The CV heads have larger ports so it's not all about the carbs. And you need to watch the compression ratio using big bore kits and stock heads so you guys might want to do some research on the overbore 650 cylinder business.

Good luck and please upload lots of photos for us as you go along!

Yeah. That's why we are going to use the 78 head for his build, because the VM carbs don't fit the later heads. I'll have to look again, but i seem to remember the porst actually being smaller and longer in the CV carb heads. Probably to keep velocity and vacuum up a bit to operate the vacuum controlled carbs. I might have this backwards, though.

The combustion chambers look pretty good, and is probably ok for 10:1 or 10.5:1 CR on the high octane pump gas.

The regular GS's are absurdly low CR stock. 8.6:1.

The 650 is 9.4:1 stock. The shaving of the head will probably bring it right on up around to 10:1 in my bike, which should still be fine.

[Suzuki_Don]

I would only get the head skimmed to make it true, you don't need any extra compression at 9.4:1 and you can get by on 95 octane pump fuel. I have ridden this bike on the road and it will pull from 20mph to 120+ in sixth gear and acceleration is really brisk over 3000rpm. This motor with conversion pulls really hard, more power than I will ever need. It is a 49% increase in hp.

Also I would not gear down by adding extra teeth to the rear sprocket. I added one extra tooth to the gearbox sprocket Which equates to three on the rear) and it is still geared too low. With that gearing 4,500rpm is 65mph.

[mlinder]

I always need extra compression

Here's a pic of our 12.5:1 CB350 pistons and head :P


(piston on the left is 12.5:1, the one on the right is a 'special' we've been working on, probably 11:1 or a little higher.)


There are quite a few people running over 10:1 on the Honda SOHC4's, and honestly, the head design is not nearly as good on those as these GS's, so I can't see it being a problem.

I'm sure it's plenty fast, Don, and since I'm shaving it for level anyway, I may as well get a tad of a bump out of it.

I'll be putting the 2-up the on the bike while it's still a 550. I'll figure out where I want it after the 650 engine is in. I'll probably go back to stock gearing.

It's really just a matter of principle. No reason not to, so far as I can see, and it doesn't cost anything extra...


By the way, Don, you mentioned you had some info on your conversion that was not on this site, can I get a link or two?